IE 8 does not display alt text in a tooltip
One of the good things about IE 8 is that—in standards mode—it no longer displays
alt text in a tooltip. Previous versions of Internet Explorer do that when you hover the mouse cursor over an image, and this has led to many people misunderstanding the
alt attribute and writing bad alt texts.
It’s good that this has finally been fixed and that IE 8 now behaves like other browsers when images are visible (what happens when images are disabled, missing or broken is another story).
The downside of it is that you may need to explain to clients why their tooltips are gone. Take the chance to tell them about Writing good alt text and that they should use the
title attribute if they want something to appear as a tooltip. However, also make sure you Don’t use the title attribute for essential information.